After more than 10 years of research and development, the external quantum efficiency of UVLED under 280nm has exceeded 5%, the corresponding luminous power is greater than 5mW, and the lifespan is up to 10000h. Deep uv leds are used for optical sensors and instruments (230~400 nm), uv authentication, bar code (230~280 nm), drinking water sterilization, and portable sterilization (240~280 nm). But deep uv has some problems.
1. Low power?
The external quantum efficiency of deep uv LED has exceeded 5%, but it is still very low compared with 60% of blue light. The reasons are as follows.
(1) quality defects of template materials. The dislocation density of A1N material epitaxial on sapphire is as high as 1X109cm2, while the dislocation density of GaN material growing on graphic substrate is about 1x107cm2. Therefore, graph substrate is adopted to improve the quality of template material.
(2) the total internal reflection loss of deep ultraviolet light in the multi-layer structure and the absorption of p-type electrode lead to poor optical extraction efficiency, which is only 6% at present. A breakthrough in contact with p-type ohms is required to reduce the dependence on high-absorbing p-gan; To optimize the refractive index difference of multilayer heterojunction; Using a graphic substrate; Coarsen the glossy surface.
(3) the A1GaN of the high-alumina component will have significant polarization effect, which will lead to polarization electric field in the quantum well and barrier, resulting in increased working voltage and decreased quantum efficiency. The solution is to use non-polar surface (e.g., surface a) sapphire as the substrate, or use component gradient method to offset.
The UVC LED power produced by LG has reached 100mW. Life can also reach 10000h.
2. Poor heat dissipation
The low efficiency of external quantum makes most electric energy into thermal energy, so the problem of heat dissipation is very important. From the perspective of chip and packaging, the film flip deep uv LED and reverse welding deep uv LED can improve heat dissipation and make high power deep uv LED.
3. Low life
Compared with the 100000h of blue light, the service life of deep uv LED is only 10000h. The low service life of LED is mainly attributed to the material defects and poor heat dissipation, as well as the aging of packaging materials when exposed to ultraviolet light.